This invention relates to a device comprising: an electronic circuit with a first test connection, a means with an output for supplying a signal input of the electronic circuit with a fixed logic value in an operational mode, and an electric interconnection between the output and the signal input. A known example of such a means is a pull-up resistor for applying a logic "1" as a fixed value to a non-used input of an IC.
Inputs which are to receive a fixed value in logic circuits are usually provided with so-called pull-up or pull-down resistors. A resistor of this kind is connected to the relevant input on the one side and to a fixed voltage on the other side. Leaving inputs open is not permissible, inter alia because oscillations which are liable to damage the IC may then arise. Direct connection of the relevant input to a fixed voltage usually is not permitted. From the point of view of testability, a special test point on the conductor and a resistor are often prescribed.
Logic circuits utilize integrated circuits (ICs) which increasingly comprise Boundary Scan Test (BST) logic. These ICs enable the testing of the interconnection function of the circuit support in conformity with the BST method. See pages 1 to 17 of the book "Boundary-Scan Test, A Practical Approach", Harry Bleeker, Peter van den Eijnden and Frans de Jong, Kluwer Academic Publishers, Boston, US, 1993, ISBN 0-7923-9296-5 for a description of the testing according to the BST method.
In order to enable complete testing of an interconnection, all connection points should be connected to ICs provided with BST logic or other logic capable of generating or analysing test data. This implies that the interconnection between the above-mentioned input to a pull-up or pull-down resistor cannot be tested by way of the BST method because resistors do not comprise test logic.